Systems and Methods for Regenerating Data from a Defective Medium

ABSTRACT

Various embodiments of the present invention provide systems and methods for data regeneration. For example, a system for data regeneration is disclosed that includes a data input derived from the medium. A data detector and a data recovery system receive the data input. The data detector provides a first soft output, and the data recovery system provides a second soft output. The first soft output and the second soft output are provided to a multiplexer. A media defect detector performs a media defect detection process, and provides a defect flag that indicates whether the data input is derived form a defective portion of the medium. The defect flag is provided to the multiplexer where it is used to select whether the first soft output or the second soft output is provides as an extrinsic output.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to (is a non-provisional of)U.S. Provisional Patent Application No. 61/037,017 entitled “Systems andMethods for Regenerating Data from a Defective Medium”, and filed Mar.17, 2008 by Tan et al. The entirety of the aforementioned application isincorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present inventions are related to systems and methods fortransferring information, and more particularly to systems and methodsfor obtaining data from defective media associated with a data transfer.

Various data transfer systems have been developed including storagesystems, cellular telephone systems, radio transmission systems. In eachof the systems data is transferred from a sender to a receiver via somemedium. For example, in a storage system, data is sent from a sender(i.e., a write function) to a receiver (i.e., a read function) via astorage medium. The effectiveness of any transfer is impacted by anydefects associated with the transfer medium. In some cases, data losscaused by defects in the transfer medium (e.g., a physical defect ornoise associated therewith) can make recovery of data from the transfermedium difficult even for data received from non-defective areas ortimes.

Various approaches have been developed for identifying defects in atransfer medium. In such systems, the identification of a potentialdefect causes a resulting nullification of any data derived from a givendefective area of a medium. By nullifying the data, errors are notallowed to propagate through later processing steps. Turning to FIG. 1,an example of a system 100 capable of nullifying data is depicted.System 100 includes a digital filter (DFIR) 115 that receives a mediadata input 105 and provides a filtered version of media input 105 to adetector 120. Detector 120 performs a data detection algorithm andprovides an output 170 that includes both a soft output and a hardoutput. In addition, system 100 includes a defect detector 110 that isoperable to identify a period when the medium from which media datainput 105 is derived is possibly defective. When a potentially defectiveregion is identified, an output 112 is asserted high causing amultiplexer 125 to select a nullified data set 160 to replace output 170from detector 120. The output of multiplexer 125 is provided to aninterleaver 130 that interleaves the data and provides the interleaveddata to a decoder 140. Decoder 140 performs a decoding algorithm on thedata and provides a data output 150. In some cases, data output 150 isde-interleaved using a de-interleaver 135 and fed back to detector 120where it is reprocessed on a subsequent iteration. While system 100provides for nullifying data derived from a potentially defecting regionof a medium thereby reducing the possibility of error propagation, itfails to obtain any data from the defective region. In some cases, thisis not acceptable as data from the defective region may be highlydesirable for one reason or another.

Hence, for at least the aforementioned reasons, there exists a need inthe art for advanced systems and methods for obtaining data frompotentially defective media.

BRIEF SUMMARY OF THE INVENTION

The present inventions are related to systems and methods fortransferring information, and more particularly to systems and methodsfor obtaining data from defective media associated with a data transfer.

Various embodiments of the present invention provide systems forregenerating data derived from a defective portion of a medium. Suchsystems include a data input derived from the medium. A data detectorand a data recovery system receive the data input. The data detectorprovides a first soft output, and the data recovery system provides asecond soft output. The first soft output and the second soft output areprovided to a multiplexer. A media defect detector performs a mediadefect detection process, and provides a defect flag that indicateswhether the data input is derived form a defective portion of themedium. The defect flag is provided to the multiplexer where it is usedto select whether the first soft output or the second soft output isprovides as an extrinsic output. In some cases, the first soft output isgenerally more accurate than the second soft output when a defectiveportion of the medium is indicated. In some cases, the detector is asoft output noise predictive maximum likelihood detector. The medium maybe, but is not limited to, a magnetic storage medium, a wirelesscommunication channel, or a wired communication channel.

In some instances of the aforementioned embodiments, the data recoverysystem includes an equalizer and a soft LLR estimator. The equalizerprovides an equalized output indicating a polarity of the data input.The soft LLR estimator receives the equalized output and provides athird soft output corresponding to the equalized output. The third softoutput may be provided as the second soft output as is, or may befurther manipulated before being provided as the second soft output. Insome cases, the soft LLR estimator multiplies the equalized output by ascalar value. The equalizer may be, but is not limited to, a fullresponse equalizer, a zero force equalizer, or an MMSE equalizer.

In various cases, the data input is precoded. In such cases, the datarecovery system further includes a two state MAP deprecoder thatreceives the third soft output and deprecodes the third soft output togenerate the second soft output. As used herein, the phrase “two stateMAP decoder” is used in its broadest sense to mean any two stateconvolutional code decoder including, but not limited to, a maximum aposteriori decoder or a soft output Viterbi algorithm decoder. A decoderreceives an intrinsic input and generates an extrinsic output. Theextrinsic output is provided along with the third soft output to the twostate MAP deprecoder. As used herein, the terms “intrinsic” and“extrinsic” are used in their general sense. In general, blocks includeboth an intrinsic input and an extrinsic output. In various cases, theextrinsic output from one block may be the intrinsic input of anotherblock. Similarly, where a block feeds information back to itself, anextrinsic output from the block may be the intrinsic input to the sameblock.

Other embodiments of the present invention provide methods forregenerating data derived from a defective portion of a medium. Suchmethods include receiving a data input derived from a medium, performinga data detection on the data input to generate a first soft output,performing a data regeneration process on the data input to generate asecond soft output, determining a defect status of the medium, and basedat least in part on the determination of the defect status of themedium, selecting either the first soft output or the second soft outputfor decoding.

This summary provides only a general outline of some embodiments of theinvention. Many other objects, features, advantages and otherembodiments of the invention will become more fully apparent from thefollowing detailed description, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the various embodiments of the presentinvention may be realized by reference to the figures which aredescribed in remaining portions of the specification. In the figures,like reference numerals are used throughout several drawings to refer tosimilar components. In some instances, a sub-label consisting of a lowercase letter is associated with a reference numeral to denote one ofmultiple similar components. When reference is made to a referencenumeral without specification to an existing sub-label, it is intendedto refer to all such multiple similar components.

FIG. 1 a prior art data cancellation system;

FIG. 2 a data recovery system that may be used in relation to variousembodiments of the present invention;

FIG. 3 depicts a full response re-equalization circuit that may be usedin relation to various embodiments of the present invention;

FIGS. 4 a-4 b depicts exemplary data plots showing a defective mediaregion, DFIR samples and ZFE samples that aid in discussion of thevarious embodiments of the present invention;

FIG. 5 shows a data regeneration system in accordance with one or moreembodiments of the present invention;

FIG. 6 shows another data regeneration system in accordance with one ormore embodiments of the present invention;

FIG. 7 depicts another data regeneration system in accordance with otherembodiments of the present invention;

FIG. 8 depicts yet another data regeneration system in accordance withyet other embodiments of the present invention;

FIG. 9 shows a storage system including a media defect detection anddata regeneration system in accordance with various embodiments of thepresent invention;

FIG. 10 depicts a communication system including a media defectdetection and data regeneration system in accordance with one or moreembodiments of the present invention;

FIG. 11 depicts another data regeneration system in accordance withother embodiments of the present invention; and

FIG. 12 shows yet another data regeneration system in accordance withyet other embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions are related to systems and methods fortransferring information, and more particularly to systems and methodsfor obtaining data from defective media associated with a data transfer.

Media defect detection is a key operation in a magnetic recordingsystem. If not appropriately handled, data derived from an undetectedregion of a medium can degrade or even disable such a magnetic recordingsystem. This is particularly true for a read channel using iterativedecoding. It should be noted that while various embodiments of thepresent invention are described in relation to a magnetic recodingchannel, various embodiments of the present invention may be applied toother types of channels including, but not limited to, communicationchannels. Embodiments of the present invention provide mechanisms forreducing the possibility of propagating errors from a potentiallydefective portion of a medium as indicated by a media defect detector.In the embodiments, the data from the potentially defective medium isnot simply nullified, but rather is manipulated to salvage at least someindication of the original data written to the medium. This indicia ofthe original data written to the medium may be used in subsequentiterations of a detection and decoding process that aid in recoveringthe data from the potentially defective region of the medium. While suchembodiments have been describes as being particularly applicable tomagnetic recording systems, one of ordinary skill in the art willrecognize other systems such as, for example, communication systems towhich data recovery in accordance with one or more embodiments of thepresent invention may be applied. Some embodiments of the presentinvention use techniques to improve the correction of data derived froma defective portion of a medium or channel. In some such embodiments,otherwise wasted data derived from a defective portion of a channel isre-equalized to full response. By doing so, the obtained residue may beat least partially utilized to correct and/or recover data derived froma defective portion.

Turning to FIG. 2, a data recovery system 200 that may be used inrelation to various embodiments of the present invention is shown. Datarecovery system 200 includes an analog to digital converter 210 thatreceives an analog media data input 205 and converts it to acorresponding digital media data input 215. Analog to digital converter210 may be any circuit known in the art that is capable of receiving ananalog signal and converting the analog signal to a digital signal.Analog media data input 205 is an analog data signal derived from somemedium. The medium may be, but is not limited to, a magnetic storagemedium, a wireless communication channel, a wired communication channel,or the like. Based on the disclosure provided herein, one of ordinaryskill in the art will recognize a variety of media from which analogmedia data input (or a digital media data input) may be derived. Digitalmedia data input 215 is provided to a digital filter 220 (DFIR) as isknown in the art.

The output of digital filter 220 is provided to a detector 225 and to anequalizer 230. Detector 225 may be any detector known in the artincluding, but not limited to, a soft output viterbi algorithm (SOVA)detector or a maximum a posteriori (MAP) detector. Detector 225 providesboth a hard output 250 and a soft output 255. Equalizer 230 provides ahard output 260. A soft output estimator 235 provides a soft output 265that corresponds to hard output 260 and is reduced substantially torecognize the reduced probability of the accuracy of equalizer 230 whena media defect flag (not shown) is asserted. The media defect flag maybe asserted whenever a potential defect is detected related to a mediumfrom which analog media data input 205 is derived. The media defect flagmay be asserted by any media defect detector known in the art. Exemplarymedia defect detectors are disclosed in PCT Patent Application No.PCT/US07/80043 entitled “Systems and Methods for Media Defect Detection”and filed on Oct. 1, 2007 by Agere Systems Inc. The entirety of theaforementioned patent application is incorporated herein by referencefor all purposes. It should be noted that other types a media defectdetection may be used in relation to the various embodiments of thepresent invention. In one particular embodiment of the presentinvention, soft output estimator 235 may simply provide a hardwiredvalue representing a relatively low probability of accuracy of hardoutput 260. As an example, the hardwired soft output may represent, forexample, a twenty-five percent probability of accuracy. Based on thedisclosure provided herein, one of ordinary skill in the art willrecognize a variety of probabilities that may be generated by softoutput estimator 235 in accordance with different embodiments of thepresent invention.

In some particular embodiments of the present invention, equalizer 230may utilize a full response equalization circuit. Turning to FIG. 3, anexample, of such a full response re-equalization circuit 320 is shown inrelation to a magnetic recording channel 300. An output 315 of ananalog-to-digital converter 310 is first equalized to a pre-set PRtarget using a PR equalizer 330. PR equalizer may be implemented as aDFIR. PR equalizer 330 is adaptive and may be driven by a first noisepredictive maximum likelihood (NPML) detector 340 to yield a harddecision, {circumflex over (x)}_(i). As shown in FIG. 3, full-responseequalizer 320 is added upon PR equalizer 330. Full-response equalizer320 can also be driven by NPML detector 340 via hard decision{circumflex over (x)}_(i). In addition, a known data training mode usinga PR target 390 is also available which uses know data, x_(i), andy_(ideal,i) to adapt the equalizer. Such a full response equalizationcircuit may be used to remove or reduce inter-symbol interference (ISI)and is capable of deriving meaningful information from digital mediadata input 215 at times when a media defect is indicated. In particular,such a full response equalizer is capable of deriving the polarity of asignal with some reasonable level of accuracy. During such times,detector 225 is not capable of providing meaningful information fromdigital media data input 215. Thus, some embodiments of the presentinvention replace the output from detector 225 with the polarity datafrom equalizer 230. During times when a media defect is not indicated,the output from detector 225 is used as it contains not only reasonablyaccurate polarity information, but also reasonably accurate magnitudeinformation.

In another particular embodiment of the present invention, equalizer 230is a zero force equalizer (ZFE) as are known in the art that attempts toremove inter-symbol interference (ISI) and is capable of derivingmeaningful information from digital media data input 215 at times when amedia defect is indicated. In particular, such a zero force equalizer iscapable of deriving the polarity of a signal with some reasonable levelof accuracy. During such times, detector 225 is not capable of providingmeaningful information from digital media data input 215. Thus, someembodiments of the present invention replace the output from detector225 with the polarity data from equalizer 230. During times when a mediadefect is not indicated, the output from detector 225 is used as itcontains not only reasonably accurate polarity information, but alsoreasonably accurate magnitude information.

The aforementioned zero force equalizer provides hard output 260 that isrepresented by the following equation:

${z_{i} = {{\sum\limits_{k = {- K}}^{K}{y_{i - k}w_{k}}} = {{q_{0}x_{i}} + {\sum\limits_{k = {- {K{({k \neq 0})}}}}^{M + K - 1}{q_{k}x_{i - k}}} + {\sum\limits_{k = {- K}}^{K}{w_{k}n_{i - k}}}}}},$

where n_(i) is the overall noise, and the zero forcing filter isw=[w_(−K), w_(−K+1), . . . , w_(K−1), w_(K)]. The equalizer output isminimized by forcing the equalizer response to the following:

$q_{k} = \left\{ \begin{matrix}{1,} & {k = 0} \\{0,} & {{k \neq 0},}\end{matrix} \right.$

which is commonly known as the zero force equalizer criterion. Byimposing the following condition E{(x_(i)−z_(i))x_(i-k)}=0, the zeroforce equalizer can be implemented as follows:

w _(K) ^(i+1) =w _(k) ^(i)+Δ(x _(i) −z _(i))x _(i-k) , i=0, 1, 2 . . .

In a decision driven mode, x_(i) is unknown and can be replaced bydecision {circumflex over (x)}_(i).

In yet another particular embodiment of the present invention, equalizer230 is a minimum mean-square error (MMSE) equalizer as are known in theart that attempts to remove inter-symbol interference (ISI) and iscapable of deriving meaningful information from digital media data input215 at times when a media defect is indicated. In particular, such anMMSE equalizer is capable of deriving the polarity of a signal with somereasonable level of accuracy. During such times, detector 225 is notcapable of providing meaningful information from digital media datainput 215. Thus, some embodiments of the present invention replace theoutput from detector 225 with the polarity data from equalizer 230.During times when a media defect is not indicated, the output fromdetector 225 is used as it contains not only reasonably accuratepolarity information, but also reasonably accurate magnitudeinformation.

The aforementioned MMSE equalizer uses the following criterion tominimize:

$J = {{E\left\{ {{x_{i} - z_{i}}}^{2} \right\}} = {E{\left\{ {{x_{i} - {\sum\limits_{k = {- K}}^{K}{y_{i - k}w_{k}}}}}^{2} \right\}.}}}$

The aforementioned criterion is used in place of that described above inrelation to zero force equalization. Of note, the desired output, x_(i),indicates this is a full-response equalizer. Accordingly, the adaptationis different that described above in relation to zero forceequalization, and is written as follows:

w _(k) ^(i+1) =w _(k) ^(i)+Δ(_(i) −z _(i))y _(i-k) , i=0, 1, 2, . . .

Turning to FIGS. 4 a-4 b, exemplary data plots show a defective mediaregion, DFIR samples and ZFE samples that aid in discussion of thevarious embodiments of the present invention. It should be noticed thatwhile these figures depict exemplary results achievable using a zeroforce equalizer in place of equalizer 230, similar exemplary results maybe achieved through use of full response equalization or MMSEequalization as described above. First, turning to FIG. 4 a, the outputof filter 220 are shown for three distinct regions of a medium fromwhich analog media data input 205 is derived: (1) an initialnon-defective region 311, (2) a subsequent non-defective region 331, and(3) an intervening defective region 321. As shown, the output of filter220 provides good four level differentiation (i.e., a two tap partialresponse) during non-defective regions 311, 331. In contrast, duringdefective region 321, the signals become very difficult todifferentiate. This inability to differentiate typically renders theoutput of detector 225 highly inaccurate. Turning to FIG. 4 b, a plot341 of the output of filter 321 is shown that corresponds to that shownin non-defective regions 311, 331. Another plot 351 shows the output ofequalizer 230 (i.e., a single tap target). The output of plot 351provides similar polarity information for both defective region 321 andnon-defective regions 311, 331. As shown by plot 341, the output ofdigital filter 220 provides some reasonable information about the datareceived from defective region 320, albeit not as rich as theinformation available from detector 225 during non-defective regions311, 331.

Turning to FIG. 5, a data regeneration system 500 operating on anon-precoded channel is depicted in accordance with various embodimentsof the present invention. Of note, only the decoding side of the circuitis depicted and it is understood that an encoder and medium would existfrom which a data input 505 is derived. Data regeneration system 500includes data input 505 that may be received, for example, from ananalog to digital converter (not shown). Data input 505 is provided to aPR equalizer 510 as is known in the art (PR equalizer may be implementedas a DFIR), and to a defect detector 515 as is known in the art. Defectdetector 515 may be operable to determine that a medium from which datainput 505 is derived has a defective region. When a defective region isdetected, defect detector 515 asserts a media defect flag 520 thatcontrols selection of a multiplexer 540. Multiplexer 540 provides anextrinsic log likelihood ratio (LLR) 545 to a decoder 570. In somecases, decoder 570 is a low density parity check (LDPC) decoder as isknown in the art. In particular, when media defect flag 520 is assertedsuch that a defective portion of a medium from which data input 505 isindicated, an output 525 is selected. In contrast, when media defectflag 520 is asserted such that a media defect is not indicated, output530 is selected.

As some examples, defect detector 515 may be defect detector similar tothose disclosed in PCT Patent Application No. PCT/US07/80043 entitled“Systems and Methods for Media Defect Detection” and filed on Oct. 1,2007 by Agere Systems Inc. The entirety of the aforementioned patentapplication was previously incorporated herein by reference for allpurposes. It should be noted that other types a media defect detectionmay be used in relation to the various embodiments of the presentinvention.

Output 530 is driven by a soft output detector 550 as are known in theart, and output 525 are driven by an equalizer 560 that may be similarto those described above. In one particular embodiment of the presentinvention, equalizer 560 is a zero force equalizer similar to thatdescribed above. An output 502 of PR equalizer 510 is provided to bothsoft output detector 550 and equalizer 560. Soft output detector 550performs a detection algorithm on the received input and provides output530 as is known in the art. Output 530 provides at least a softindication of the original data that was previously encoded and fromwhich data input 505 is derived. When the medium from which data input505 is derived is non-defective, output 530 provides a reasonablyaccurate representation of the originally encoded data. In contrast,when the medium from which data input 505 is derived is defective,output 530 becomes less accurate and in some cases the decreasedaccuracy results in an inability for decoder 570 to operate properly. Anextrinsic LLR output 575 from decoder 570 is fed back to soft outputdetector 550 to be used as an intrinsic LLR input on the next iteration.

Because the inaccuracy of output 530 becomes problematic for decoder 570during times when a media defect is detected, output 525 is selected todrive extrinsic LLR 545 in place of output 530 during such times. Output525 is driven by a separate, parallel data path providing equalization.In particular, equalizer 560 performs an equalization on output 502 thatyields useful polarity information by removing inter-symbolinterference. The output of equalizer 560 is provided to a soft LLRestimator 565 that is used to convert the equalized samples fromequalizer 560 to an LLR. In some cases, soft LLR estimator 565 is ascalar β that scales an input z_(i) down to obtain an output Λ_(i). Saidanother way, soft LLR estimator 565 provides a soft output comparable tothat provided by soft output detector 550, albeit a soft outputindicating a generally reduced probability of accuracy when comparedwith that available from soft output detector 550 when a media defect isnot indicated. In some cases, the output from soft LLR estimator 565 maybe provided directly to multiplexer 640 to be used in place of output530 when a media defect is detected.

In some cases such as the case that is shown, intrinsic LLR 575 may beused to further massage the output of soft LLR estimator 565. Inparticular, intrinsic LLR 575 is multiplied by a multiplier 508 (alpha)using a multiplier 509. The product of multiplier 509 is added to theoutput of soft LLR estimator 565 using an adder 511. The product ofadder 511 is output 525. Where such is the case, the following equationdescribes the extrinsic LLR 545 (i.e., the soft input) that is providedto decoder 570:

${\Lambda_{{ldpc},a}^{j + 1}\left( x_{i} \right)} = \left\{ \begin{matrix}{{\Lambda_{{ch},{ext}}^{j}\left( x_{i} \right)},} & {{where}\mspace{14mu} {defect}\mspace{14mu} {flag}\mspace{14mu} 520\mspace{14mu} {does}\mspace{14mu} {not}\mspace{14mu} {intricate}\mspace{14mu} a\mspace{14mu} {defect}} \\{{{\beta \cdot z_{i}} + {\alpha \cdot {\Lambda_{{ldpc},{ext}}^{j}\left( x_{i} \right)}}},} & {{where}\mspace{14mu} {defect}\mspace{14mu} {flag}\mspace{14mu} 520\mspace{14mu} {indicates}\mspace{14mu} a\mspace{14mu} {{defect}.}}\end{matrix} \right.$

It should be noted that regardless of whether output 525, output 530, orthe output of soft LLR estimator 565 is chosen to drive extrinsic LLR545, decoder 570 may apply the same decoding process. In some cases, thedecoding process is a standard LDPC decoding process.

Turning to FIG. 6, a data regeneration system 600 operating on anon-precoded channel is depicted in accordance with various embodimentsof the present invention. Of note, only the decoding side of the circuitis depicted and it is understood that an encoder and medium would existfrom which a data input 605 is derived. Data regeneration system 600includes data input 605 that may be received, for example, from ananalog to digital converter (not shown). Data input 605 is provided to aPR equalizer 610 as is known in the art, and to a defect detector 615 asis known in the art. Defect detector 615 may be operable to determinethat a medium from which data input 605 is derived has a defectiveregion. When a defective region is detected, defect detector 615 assertsa media defect flag 620 that controls selection of a multiplexer 640.Multiplexer 640 provides an extrinsic log likelihood ratio (LLR) 645 toa decoder 670. In some cases, decoder 670 is a low density parity check(LDPC) decoder as is known in the art. In particular, when media defectflag 620 is asserted such that a defective portion of a medium fromwhich data input 605 is indicated, an output 625 is selected. Incontrast, when media defect flag 620 is asserted such that a mediadefect is not indicated, output 630 is selected.

As some examples, defect detector 615 may be defect detector similar tothose disclosed in PCT Patent Application No. PCT/US07/80043 entitled“Systems and Methods for Media Defect Detection” and filed on Oct. 1,2007 by Agere Systems Inc. The entirety of the aforementioned patentapplication was previously incorporated herein by reference for allpurposes. It should be noted that other types a media defect detectionmay be used in relation to the various embodiments of the presentinvention.

Output 630 is driven by a soft output detector 650 as are known in theart, and output 625 are driven by a full response equalizer 660 that maybe similar to those described above. In one particular embodiment of thepresent invention, full response equalizer 660 is a 6-tap FIR filter. Anoutput 602 of PR equalizer 610 is provided to both soft output detector650 and full response equalizer 660. Soft output detector 650 performs adetection algorithm on the received input and provides output 630 as isknown in the art. Output 630 provides at least a soft indication of theoriginal data that was previously encoded and from which data input 605is derived. When the medium from which data input 605 is derived isnon-defective, output 630 provides a reasonably accurate representationof the originally encoded data. In contrast, when the medium from whichdata input 605 is derived is defective, output 630 becomes less accurateand in some cases the decreased accuracy results in an inability fordecoder 670 to operate properly. An intrinsic LLR output 675 fromdecoder 670 is fed back to soft output detector 650 to allow foriterative processing.

As the inaccuracy of output 630 becomes problematic for decoder 670during times when a media defect is detected, output 625 is selected todrive extrinsic LLR 645 during such times. Output 625 is driven by aseparate, parallel data path providing full response equalization. Inparticular, full response equalizer 660 performs an equalization onoutput 602 that yields useful polarity information by removinginter-symbol interference. The output of full response equalizer 660 isprovided to a soft LLR estimator 665 that is used to convert theequalized samples from full response equalizer 660 to an LLR. In somecases, soft LLR estimator 665 is a scalar β that scales an input z_(i)down to obtain an output Λ_(i). Said another way, soft LLR estimator 665provides a soft output comparable to that provided by soft outputdetector 650, albeit a soft output indicating a generally reducedprobability of accuracy when compared with that available from softoutput detector 650 when a media defect is not indicated. In some cases,the output from soft LLR estimator 665 may be provided directly tomultiplexer 640 to be used in place of output 630 when a media defect isdetected.

In some cases such as the case that is shown, intrinsic LLR 675 may beused to further massage the output of soft LLR estimator 665. Inparticular, intrinsic LLR 675 is multiplied by a multiplier 608 (alpha)using a multiplier 609. The product of multiplier 609 is added to theoutput of soft LLR estimator 665 using an adder 611. The product ofadder 611 is output 625. Where such is the case, the following equationdescribes the extrinsic LLR 645 (i.e., the soft input) that is providedto decoder 670:

${\Lambda_{{ldpc},a}^{j + 1}\left( x_{i} \right)} = \left\{ \begin{matrix}{{\Lambda_{{ch},{ext}}^{j}\left( x_{i} \right)},{{where}\mspace{14mu} {defect}\mspace{14mu} {flag}\mspace{14mu} 620\mspace{14mu} {does}\mspace{14mu} {not}\mspace{14mu} {indicate}\mspace{14mu} a\mspace{14mu} {defect}}} \\{{{\beta \cdot z_{i}} + {\alpha \cdot {\Lambda_{{ldpc},{ext}}^{j}\left( x_{i} \right)}}},{{where}\mspace{14mu} {defect}\mspace{14mu} {flag}\mspace{14mu} 620\mspace{14mu} {indicates}\mspace{14mu} a\mspace{14mu} {{defect}.}}}\end{matrix} \right.$

It should be noted that regardless of whether output 625, output 630, orthe output of soft LLR estimator 665 is chosen to drive extrinsic LLR645, decoder 670 may apply the same decoding process. In some cases, thedecoding process is a standard LDPC decoding process.

Turning to FIG. 7, another data regeneration system 700 operating on aprecoded channel is depicted in accordance with other embodiments of thepresent invention. Data regeneration system 700 includes an originaldata input 702 that is provided to an encoder 704 where it is encoded asis known in the art. In one case, encoder 704 is an LDPC encoder. Theencoded data is then precoded by a precoder 706. In one particularembodiment of the present invention, precoder 706 applies a 1/(1+D)precoding to the received encoded data. The precoded data is provided toa channel 708 from which a data input 710 is derived. Channel 708 may beany medium by which information is transferred including, but notlimited to, a magnetic storage medium, a atmosphere through whichsignals are transferred, an electrically or optically conductivematerial by which signals may be transferred or the like. Based on thedisclosure provided herein, one of ordinary skill in the art willrecognize a variety of media that may comprise channel 708.

Data input 710 may be converted using an analog to digital converter711. Data input 710 is provided to a PR equalizer 714 as is known in theart. PR equalizer 714 may be implemented as a DFIR. An output 716 fromPR equalizer 714 is provided to a defect detector 722 that may beoperable to determine that a medium (i.e., channel 708) from which datainput 710 is derived has a defective area, region or time period. When adefective portion is detected, defect detector 722 asserts a mediadefect flag 724 that controls selection of a multiplexer 746.Multiplexer 746 provides an extrinsic LLR 750 to a decoder 754. Decoder754 provides a decoding process that is complementary to encoder 704. Insome cases, decoder 754 is an LDPC decoder as is known in the art. Inparticular, when media defect flag 724 is asserted such that a defectiveportion of a medium from which data input 710 is indicated, an output766 is selected. In contrast, when media defect flag 724 is assertedsuch that a media defect is not indicated, output 770 is selected.

As some examples, defect detector 722 may be defect detector similar tothose disclosed in PCT Patent Application No. PCT/US07/80043 entitled“Systems and Methods for Media Defect Detection” and filed on Oct. 1,2007 by Agere Systems Inc. The entirety of the aforementioned patentapplication was previously incorporated herein by reference for allpurposes. It should be noted that other types a media defect detectionmay be used in relation to the various embodiments of the presentinvention.

Output 770 is driven by a soft output detector 762 as are known in theart, and output 766 are driven by a full response equalizer 718 that maybe similar to those described above. In one particular embodiment of thepresent invention, full response equalizer 718 is a 6-tap FIR filter. Anoutput 716 of PR equalizer 714 is provided to both soft output detector762 and full response equalizer 718. Soft output detector 762 performs adetection algorithm on the received input and provides output 770 as isknown in the art. Output 770 provides at least a soft indication oforiginal data 702 that was previously encoded and from which data input710 is derived. When the medium from which data input 710 is derived isnon-defective, output 770 provides a reasonably accurate representationof the originally encoded data. In contrast, when the medium from whichdata input 710 is derived is defective, output 770 becomes less accurateand in some cases the decreased accuracy results in an inability fordecoder 754 to operate properly. An intrinsic LLR output 758 fromdecoder 754 is fed back to soft output detector 762 to allow foriterative processing.

As the inaccuracy of output 770 becomes problematic for decoder 754during times when a media defect is detected, output 766 is selected todrive extrinsic LLR 750 during such times. Output 766 is driven by aseparate, parallel data path providing full response equalization. Inparticular, full response equalizer 718 performs an equalization onoutput 716 that yields useful polarity information by removinginter-symbol interference. The output of full response equalizer 718 isprovided to a soft LLR estimator 726 that is used to convert theequalized samples from full response equalizer 718 to an LLR. In somecases, soft LLR estimator 726 is a scalar β that scales an input z_(i)down to obtain an output Λ_(i). Said another way, soft LLR estimator 726provides a soft output comparable to that provided by soft outputdetector 726, albeit a soft output indicating a generally reducedprobability of accuracy when compared with that available from softoutput detector 762 when a media defect is not indicated. In some cases,the output from soft LLR estimator 726 may be provided directly tomultiplexer 746 to be used in place of output 770 when a media defect isdetected.

In contrast to the non-coded channel approach, in the precoded channel,soft output detector 762 only provides LLRs for the data before precoder706. However, full response equalizer 718 operates on the data afterprecoder 706. Thus, soft LLR estimator 726 only provides LLRs for bitscorresponding to a media defect region after precoder 706. Decoder 754receives LLRs for the data before precoder 706 as an input. Thus, an LLRconverter is used to convert the LLRs from after precoder 706 to beforeprecoder 706. Data before precoder 706 is referred to as u_(i), and dataafter precoder 706 is referred to as x_(i). Using this convention, afterfull-response equalizer 718 and soft LLR estimator 726, it is necessaryto convert Λ_(a)(x_(i)) to Λ_(a)(u_(i)).

A method for performing the above mentioned conversion utilizes a twostate MAP deprecoder 730. Two state MAP deprecoder 730 may be, forexample, a standard soft output convolutional code decoder. Two stateMAP deprecoder 730 takes soft inputs from soft LLR estimator 726 (i.e.,Λ_(a)(x_(i))) and from decoder 754 (i.e., Λ_(a)(u_(i))), and generatessoft outputs Λ_(ext)(u_(i)) (and Λ_(ext)(x_(i)) but not needed). Twostate MAP deprecoder 730 may have a very low complexity compared withthe complexity of detector 762 as it may only demand two statescorresponding to precoder 706 where precoder 706 implements 1/(1+D). Twostate MAP deprecoder 730 does not exhibit any data dependency andtherefore does not have noise prediction. Further, two state MAPdeprecoder 730 does not take channel input in its branch metric. Inother words, the branch metric only handles soft inputs Λ_(a)(x_(i)) andΛ_(a)(u_(i)).

In some cases, the output of two state MAP deprecoder 730 is provideddirectly to multiplexer 746 as input 766. In other cases, the output oftwo state MAP deprecoder 730 is further enhanced using intrinsic LLR 758that is multiplied using a multiplier (alpha) 734 using a multiplier738. The result of the multiplication is summed with the output of twostate MAP deprecoder 730 using an adder 742. The output of adder 742 isprovided as output 766. In such case, extrinsic LLR 750 is defined bythe following equation:

$\begin{matrix}{{\Lambda_{{ldpc},a}^{j + 1}\left( x_{i} \right)} = \left\{ \begin{matrix}{{\Lambda_{{ch},{ext}}^{j}\left( u_{i} \right)},} & {{for}\mspace{14mu} {non}\text{-}{MDbits}} \\{{{{map}\; 2\left( {{\beta \cdot z_{i}},{\Lambda_{{ldpc},{ext}}^{j}\left( u_{i} \right)}} \right)} + {\alpha \cdot {\Lambda_{{idpc},{ext}}^{j}\left( u_{i} \right)}}},} & {{{for}\mspace{14mu} {MDbits}},}\end{matrix} \right.} & \;\end{matrix}$

where map2( ) represents the function of two state MAP deprecoder 730.

Turning to FIG. 8, yet another data regeneration system 800 operating ona precoded channel is depicted in accordance with other embodiments ofthe present invention. Data regeneration system 800 includes an originaldata input 802 that is provided to an encoder 804 where it is encoded asis known in the art. In one case, encoder 804 is an LDPC encoder. Theencoded data is then precoded by a precoder 806. In one particularembodiment of the present invention, precoder 806 applies a 1/(1+D)precoding to the received encoded data. The precoded data is provided toa channel 808 from which a data input 810 is derived. Channel 808 may beany medium by which information is transferred including, but notlimited to, a magnetic storage medium, a atmosphere through whichsignals are transferred, an electrically or optically conductivematerial by which signals may be transferred or the like. Based on thedisclosure provided herein, one of ordinary skill in the art willrecognize a variety of media that may comprise channel 808.

Data input 810 is received after being converted using an analog todigital converter 811. Data input 810 is provided to a PR equalizer 814as is known in the art. The output of PR equalizer 814 is provided to azero force equalizer 818, a detector 862 and to a defect detector 822.Defect detector 822 may be operable to determine that a medium (i.e.,channel 808) from which data input 810 is derived has a defective area,region or time period. When a defective portion is detected, defectdetector 822 asserts a media defect flag 824 that controls selection ofa multiplexer 846. Multiplexer 846 provides an extrinsic LLR 850 to adecoder 854. Decoder 854 provides a decoding process that iscomplementary to encoder 804. In some cases, decoder 854 is an LDPCdecoder as is known in the art. In particular, when media defect flag824 is asserted such that a defective portion of a medium from whichdata input 810 is indicated, an output 866 is selected. In contrast,when media defect flag 824 is asserted such that a media defect is notindicated, output 870 is selected.

As some examples, defect detector 822 may be defect detector similar tothose disclosed in PCT Patent Application No. PCT/US07/80043 entitled“Systems and Methods for Media Defect Detection” and filed on Oct. 1,2007 by Agere Systems Inc. The entirety of the aforementioned patentapplication was previously incorporated herein by reference for allpurposes. It should be noted that other types a media defect detectionmay be used in relation to the various embodiments of the presentinvention.

Output 870 is driven by a soft output detector 862 as are known in theart, and output 866 are driven by a zero force equalizer 818 that may besimilar to those described above. An output 816 of PR equalizer 814 isprovided to both soft output detector 862 and zero force equalizer 818.Soft output detector 862 performs a detection algorithm on the receivedinput and provides output 870 as is known in the art. Output 870provides at least a soft indication of original data 802 that waspreviously encoded and from which data input 810 is derived. When themedium from which data input 810 is derived is non-defective, output 870provides a reasonably accurate representation of the originally encodeddata. In contrast, when the medium from which data input 810 is derivedis defective, output 870 becomes less accurate and in some cases thedecreased accuracy results in an inability for decoder 854 to operateproperly. An intrinsic LLR output 858 from decoder 854 is fed back tosoft output detector 862 to allow for iterative processing.

As the inaccuracy of output 870 becomes problematic for decoder 854during times when a media defect is detected, output 866 is selected todrive extrinsic LLR 850 during such times. Output 866 is driven by aseparate, parallel data path providing full response equalization. Inparticular, zero force equalizer 818 performs an equalization on output816 that yields useful polarity information by removing inter-symbolinterference. The output of zero force equalizer 818 is provided to asoft LLR estimator 826 that is used to convert the equalized samplesfrom zero force equalizer 818 to an LLR. In some cases, soft LLRestimator 826 is a scalar β that scales an input z_(i) down to obtain anoutput Λ_(i). Said another way, soft LLR estimator 826 provides a softoutput comparable to that provided by soft output detector 826, albeit asoft output indicating a generally reduced probability of accuracy whencompared with that available from soft output detector 862 when a mediadefect is not indicated. In some cases, the output from soft LLRestimator 826 may be provided directly to multiplexer 846 to be used inplace of output 870 when a media defect is detected.

In contrast to the non-coded channel approach, in the precoded channel,soft output detector 862 only provides LLRs for the data before precoder806. However, zero force equalizer 818 operates on the data afterprecoder 806. Thus, soft LLR estimator 826 only provides LLRs for bitscorresponding to a media defect region after precoder 806. Decoder 854receives LLRs for the data before precoder 806 as an input. Thus, an LLRconverter is used to convert the LLRs from after precoder 806 to beforeprecoder 806. Data before precoder 806 is referred to as u_(i), and dataafter precoder 806 is referred to as x_(i). Using this convention, afterfull-response equalizer 818 and soft LLR estimator 826, it is necessaryto convert Λ_(a)(x_(i)) to Λ_(a)(u_(i)).

A method for performing the above mentioned conversion utilizes a twostate MAP deprecoder 830. Two state MAP deprecoder 830 may be, forexample, a standard soft output convolutional code decoder. Two stateMAP deprecoder 830 takes soft inputs from soft LLR estimator 826 (i.e.,Λ_(a)(x_(i))) and from decoder 854 (i.e., Λ_(a)(u_(i))), and generatessoft outputs Λ_(ext)(u_(i)) (and Λ_(ext)(x_(i)) but not needed). Twostate MAP deprecoder 830 may have a very low complexity compared withthe complexity of detector 862 as it may only demand two statescorresponding to precoder 806 where precoder 806 implements 1/(1+D). Twostate MAP deprecoder 830 does not exhibit any data dependency andtherefore does not have noise prediction. Further, two state MAPdeprecoder 830 does not take channel input in its branch metric. Inother words, the branch metric only handles soft inputs Λ_(a)(x_(i)) andΛ_(a)(u_(i)).

In some cases, the output of two state MAP deprecoder 830 is provideddirectly to multiplexer 846 as input 866. In other cases, the output oftwo state MAP deprecoder 830 is further enhanced using intrinsic LLR 858that is multiplied using a multiplier (alpha) 834 using a multiplier838. The result of the multiplication is summed with the output of twostate MAP deprecoder 830 using an adder 842. The output of adder 842 isprovided as output 866. In such case, extrinsic LLR 750 is defined bythe following equation:

${\Lambda_{ldpca}^{j + 1}\left( x_{i} \right)} = \left\{ \begin{matrix}{{\Lambda_{{ch},{ext}}^{j}\left( u_{i} \right)},} & {{for}\mspace{14mu} {non}\text{-}{MDbits}} \\{{{{map}\; 2\left( {{\beta \cdot z_{i}},{\Lambda_{{ldpc},{ext}}\left( u_{i} \right)}} \right)} + {\alpha \cdot {\Lambda_{{ldpc},{ext}}\left( u_{i} \right)}}},} & {{{for}\mspace{14mu} {MDbits}},}\end{matrix} \right.$

where map2( ) represents the function of two state MAP deprecoder 830.

Turning to FIG. 9, a storage system 580 including a media defect anddata regeneration system 587 is shown in accordance with variousembodiments of the present invention. Storage system 580 may be, forexample, a hard disk drive. Storage system 580 includes a read channel587 with an incorporated media defect detector and data regenerationsystem. The incorporated media defect detector may be any media defectdetector capable of detecting a defect on a disk platter 595, and thedata regeneration system may be any system capable of recovering atleast polarity data from a defective region of disk platter 595. Thus,for example, read channel 587 may incorporate a media defect detectorand data regeneration system similar to those discussed above inrelation to FIGS. 5-8. In addition, storage system 580 includes aninterface controller 585, a preamp 591, a hard disk controller 589, amotor controller 599, a spindle motor 597, a disk platter 595, and aread/write head 593. Interface controller 585 controls addressing andtiming of data to/from disk platter 595. The data on disk platter 595consists of groups of magnetic signals that may be detected byread/write head assembly 593 when the assembly is properly positionedover disk platter 595. In a typical read operation, read/write headassembly 593 is accurately positioned by motor controller 599 over adesired data track on disk platter 595. Motor controller 599 bothpositions read/write head assembly 593 in relation to disk platter 595and drives spindle motor 597 by moving read/write head assembly to theproper data track on disk platter 595 under the direction of hard diskcontroller 589. Spindle motor 597 spins disk platter 595 at a determinedspin rate (RPMs).

Once read/write head assembly 593 is positioned adjacent the proper datatrack, magnetic signals representing data on disk platter 595 are sensedby read/write head assembly 593 as disk platter 595 is rotated byspindle motor 597. The sensed magnetic signals are provided as acontinuous, minute analog signal representative of the magnetic data ondisk platter 595. This minute analog signal is transferred fromread/write head assembly 593 to read channel module 587 via preamp 591.Preamp 591 is operable to amplify the minute analog signals accessedfrom disk platter 595. In addition, preamp 591 is operable to amplifydata from read channel module 587 that is destined to be written to diskplatter 595. In turn, read channel module 587 decodes (including mediadefect detection) and digitizes the received analog signal to recreatethe information originally written to disk platter 595. This data isprovided as read data 583 to a receiving circuit. A write operation issubstantially the opposite of the preceding read operation with writedata 581 being provided to read channel module 587. This data is thenencoded and written to disk platter 595.

Turning to FIG. 10, a communication system 691 including a receiver 695with a media defect and data regeneration system in accordance with oneor more embodiments of the present invention is shown. Communicationsystem 691 includes a transmitter 693 that is operable to transmitencoded information via a transfer medium 697 as is known in the art.The encoded data is received from transfer medium 697 by receiver 695.Receiver 695 incorporates a media defect detection circuit that isoperable to determine whether a “defect” has occurred in transfer medium697, and to recover at least some level of data from the defective timeperiod or portion of transfer medium 697. Thus, for example, wheretransfer medium 697 is a wire, it may determine that no signal is beingreceived or that a disruptive level of interference is ongoing.Alternatively, where transfer medium 697 is the atmosphere carryingwireless signals, the media defect detection circuit may indicate a verynoisy and unreliable transfer environment. Based on the disclosureprovided herein, one of ordinary skill in the art will recognize avariety of mediums that may include defects and that may be utilized inrelation to different embodiments of the present invention. Theincorporated media defect detector and data regeneration system may beone such as those discussed above in relation to FIGS. 5-8.

Turning to FIG. 11, another data regeneration system 1100 is depicted inaccordance with other embodiments of the present invention. Dataregeneration system 1100 includes a DFIR 1120 and a media defectdetector 1110 that each receive a media data input 1105. The output ofDFIR 1120 is provided to a detector 1130. Detector 1130 may be, but isnot limited to, a soft output Viterbi algorithm detector or a maximum aposterior algorithm detector. The output of detector 1130 is provided asan input to a multiplexer 1180. The output of multiplexer 1140 isprovided to an interleaver 1140. The output of interleaver 1140 isprovided to a decoder 1160. The output of decoder 1160 is fed backthrough a de-interleaver 1150 to detector 1130. In addition, the outputof de-interleaver 1150 is multiplied by a value alpha 1190 using amultiplier 1185 and provided as another input to multiplexer 1180.

In operation, when a media defect is detected by media defect detector1110, the output of multiplier 1185 is selected to drive interleaver1140. In contrast, when a defect is not indicated by media defectdetector 1110, the output of detector 1130 is selected to driveinterleaver. On the first iteration, data regeneration system 1100operates consistent with that described in FIG. 1 as no data is yetavailable, but on later iterations regenerated data is provided to theof multiplexer 1180 from multiplier 1185. The following pseudo coderepresents the output provided to interleaver 1140 depending uponwhether a media defect is indicated:

IF (Media Defect Flag Indicates no Defect) { Output = (MPFIR*y-ideal)² +soft input } ELSE IF (Media Defect Flag Indicates a Defect) { Output =(1+alpha)*soft input }

Turning to FIG. 12, yet another data regeneration system 1200 is shownin accordance with yet other embodiments of the present invention. Dataregeneration system 1200 includes a DFIR 1220 and a media defectdetector 1210 that each receive a media data input 1205. The output ofDFIR 1220 is provided to a branch metric modified detector 1230. Branchmetric modified detector 1230 may be, but is not limited to, a softoutput Viterbi algorithm detector or a maximum a posterior algorithmdetector. The output of branch metric modified detector 1230 is providedto an interleaver 1240. The output of interleaver 1240 is provided to adecoder 1260, and the output of decoder 1260 is fed back to branchmetric modified detector 1220.

In operation, when a media defect is detected by media defect detector1210, the branch metric of branch metric modified detector 1230 ismodified to be: (1+alpha)*soft input. Otherwise, when no media defect isdetected by media defect detector 1210, the following standard branchmetric is used by branch metric modified detector 1230:(MPFIR*y−ideal)²+soft input. Thus, data regeneration system 1200 ismathematically equivalent to data regeneration system 1100 discussedabove.

In conclusion, the invention provides novel systems, devices, methodsand arrangements for regenerating data derived from a defective medium.While detailed descriptions of one or more embodiments of the inventionhave been given above, various alternatives, modifications, andequivalents will be apparent to those skilled in the art without varyingfrom the spirit of the invention. For example, one or more embodimentsof the present invention may be applied to various data storage systemsand digital communication systems, such as, for example, tape recordingsystems, optical disk drives, wireless systems, and digital subscribeline systems. Therefore, the above description should not be taken aslimiting the scope of the invention, which is defined by the appendedclaims.

1. A system for regenerating data derived from a defective portion of amedium, the system comprising: a data input, wherein the data input isderived from a medium; a media defect detector, wherein the media defectdetector provides a defect flag indicating a defective portion of themedium; a data detector receiving the data input and providing a firstsoft output; a data recovery system receiving the data input andproviding a second soft output; and a multiplexer, wherein themultiplexer provides either the first soft output or the second softoutput as an intrinsic input based at least in part on the defect flag.2. The system of claim 1, wherein the data recovery system includes anequalizer, and wherein the equalizer provides an equalized outputindicating a polarity of the data input.
 3. The system of claim 2,wherein the data recovery system further includes a soft estimator,wherein the soft estimator receives the equalized output and provides athird soft output corresponding to the equalized output.
 4. The systemof claim 3, wherein the soft estimator multiplies the equalized outputby a scalar value.
 5. The system of claim 3, wherein the data input isprecoded, wherein the data recovery system further includes a two stateMAP deprecoder, wherein the two state MAP deprecoder receives the thirdsoft output and deprecodes the third soft output to generate the secondsoft output.
 6. The system of claim 5, wherein the system furthercomprises: a decoder, wherein the decoder receives the intrinsic inputand decodes the intrinsic input to generate an extrinsic output, andwherein the extrinsic output is provided to the two state MAPdeprecoder.
 7. The system of claim 2, wherein the equalizer is selectedfrom a group consisting of: a full response equalizer, a zero forceequalizer, and an MMSE equalizer.
 8. The system of claim 1, wherein thefirst soft output is generally more accurate than the second soft outputwhen a defective portion of the medium is indicated.
 9. The system ofclaim 1, wherein the system further comprises: a decoder, wherein thedecoder receives the intrinsic input and decodes the intrinsic input.10. The system of claim 1, wherein the detector is a soft output noisepredictive maximum likelihood detector.
 11. The system of claim 1,wherein the medium is selected from a group consisting of: a magneticstorage medium, a wireless communication channel, and a wiredcommunication channel.
 12. A method for regenerating data derived from adefective portion of a medium, the method comprising: receiving a datainput derived from a medium; performing a data detection on the datainput, wherein a first soft output is generated; performing a dataregeneration process on the data input, wherein a second soft output isgenerated; determining a defect status of the medium; and based at leastin part on the determination of the defect status of the medium,selecting either the first soft output or the second soft output fordecoding.
 13. The method of claim 12, wherein the data recovery systemincludes an equalizer and a soft estimator, wherein the equalizerprovides an equalized output indicating a polarity of the data input,wherein the soft estimator multiplies the equalized output by a scalarvalue and provides a third soft output.
 14. The method of claim 13,wherein the third soft output is the same as the second soft output. 15.The method of claim 13, wherein the data input is precoded, wherein thedata recovery system further includes a two state MAP deprecoder,wherein the two state MAP deprecoder receives the third soft output anddeprecodes the third soft output to generate the second soft output. 16.The method of claim 13, wherein the equalizer is selected from a groupconsisting of: a full response equalizer, a zero force equalizer, and anMMSE equalizer.
 17. The method of claim 12, wherein the data detectionis performed using a soft output noise predictive maximum likelihooddetector.
 18. The method of claim 12, wherein the medium is selectedfrom a group consisting of: a magnetic storage medium, a wirelesscommunication channel, and a wired communication channel.
 19. A systemfor regenerating data derived from a defective portion of a medium, thesystem comprising: a data input, wherein the data input is derived froma medium; a media defect detector, wherein the media defect detectorprovides a defect flag indicating a defective portion of the medium; adata detector receiving the data input and providing a first softoutput; a data recovery system receiving the data input, wherein thedata recovery system includes an equalizer and a soft estimator, whereinthe equalizer provides an equalized output indicating a polarity of thedata input, and wherein the soft estimator receives the equalized outputand provides a second soft output corresponding to the data input; amultiplexer, wherein the multiplexer provides either the first softoutput or the second soft output as an intrinsic input based at least inpart on the defect flag; and a decoder, wherein the decoder decodes theintrinsic input.
 20. The system of claim 19, wherein the data input isprecoded, wherein the data recovery system further includes a two stateMAP deprecoder, wherein the two state MAP deprecoder receives the secondsoft output and the intrinsic input, and wherein the two state MAPdeprecoder deprecodes the second soft output combined with the intrinsicinput before providing the second soft output to the multiplexer.